U.S. patent application number 09/912712 was filed with the patent office on 2002-06-06 for metal halide lamp.
This patent application is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Maniwa, Takashi, Nishiura, Yoshiharu, Takeda, Kazuo.
Application Number | 20020067132 09/912712 |
Document ID | / |
Family ID | 18747597 |
Filed Date | 2002-06-06 |
United States Patent
Application |
20020067132 |
Kind Code |
A1 |
Takeda, Kazuo ; et
al. |
June 6, 2002 |
Metal halide lamp
Abstract
A metal halide lamp including a discharge tube of a transparent
ceramic in which a discharge metal and a buffer gas are sealed, the
discharge tube having electrodes at both ends thereof, including a
discharge portion, slender tube portions provided at both ends of
the discharge portion, into which feedthroughs including the
electrodes and lead-in wires are inserted, and slender tube sealing
portions in which gaps between the slender tube portions and the
feedthroughs are sealed with a sealing material, an outer tube
containing the discharge tube, and a transparent protecting
cylinder provided inside the outer tube so as to surround the
discharge tube is provided. At least one of the slender tube
sealing portions is exposed beyond the protecting cylinder. This
provides a metal halide lamp that suppresses leaks in a discharge
tube sealing portion while maintaining high efficiency and high
color rendition by using a ceramic discharge tube, and that is
tolerant of an external shock.
Inventors: |
Takeda, Kazuo; (Osaka,
JP) ; Nishiura, Yoshiharu; (Shiga, JP) ;
Maniwa, Takashi; (Osaka, JP) |
Correspondence
Address: |
Merchant & Gould P.C.
P.O. Box 2903
Minneapolis
MN
55402-0903
US
|
Assignee: |
Matsushita Electric Industrial Co.,
Ltd.
|
Family ID: |
18747597 |
Appl. No.: |
09/912712 |
Filed: |
July 25, 2001 |
Current U.S.
Class: |
315/99 ;
315/246 |
Current CPC
Class: |
H01J 61/302 20130101;
H01J 61/125 20130101; H01J 61/34 20130101; H01J 61/366 20130101;
H01J 61/827 20130101 |
Class at
Publication: |
315/99 ;
315/246 |
International
Class: |
H05B 039/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 29, 2000 |
JP |
2000-259417 |
Claims
What is claimed is:
1. A metal halide lamp comprising: a discharge tube of a
transparent ceramic in which a discharge metal and a buffer gas are
sealed, the discharge tube having electrodes at both ends thereof,
comprising; a discharge portion, slender tube portions provided at
both ends of the discharge portion, into which feedthroughs
comprising the electrodes and lead-in wires are inserted, and
slender tube sealing portions in which gaps between the slender
tube portions and the feedthroughs are sealed with a sealing
material; an outer tube containing the discharge tube; and a
transparent protecting cylinder provided inside the outer tube so
as to surround the discharge tube; wherein at least one of the
slender tube sealing portions is exposed beyond the protecting
cylinder.
2. The metal halide lamp according to claim 1, wherein the
protecting cylinder is supported within the outer tube by a
support.
3. The metal halide lamp according to claim 2, wherein an elastic
plate further is connected to the support so as to support the
slender tube portions.
4. The metal halide lamp according to claim 3, wherein the slender
tube sealing portions are provided outside a portion to be
supported by the elastic plate.
5. The metal halide lamp according to claim 3, wherein the elastic
plate is a metal, and a heat release from the slender tube sealing
portion and an insulation against a heat from the discharge portion
in the discharge tube are performed by the elastic plate.
6. The metal halide lamp according to claim 3, wherein the slender
tube portions in the discharge tube are supported by the elastic
plate, thereby reducing a shock when the lamp is dropped.
7. The metal halide lamp according to claim 1, wherein the support
is selected from the group consisting of a plate-like object and a
band-like object, and positions the protecting cylinder in the
outer tube.
8. The metal halide lamp according to claim 1, wherein the ceramic
discharge tube is rigidly supported by metal wires inside the outer
tube.
9. The metal halide lamp according to claim 1, wherein one end of
the outer tube further is provided with a stem, which seals the
outer tube airtight.
10. The metal halide lamp according to claim 1, wherein mercury,
argon as a noble gas for a starting gas, and at least one iodide
selected from the group consisting of dysprosium, thulium, holmium,
thallium and sodium as a metal halide are sealed in the discharge
tube.
11. The metal halide lamp according to claim 1, wherein a main tube
portion surrounding the discharge portion, a pair of the slender
tube portions connected to the main tube portion, into which the
lead-in wires for feeding an electricity to the electrodes are
inserted, the slender tube portion having a tip that is sealed, and
ring portions connecting the main tube portion and the slender tube
portions are sintered into one piece so as to form the ceramic
discharge tube.
12. The metal halide lamp according to claim 11, wherein the
slender tube portion has a slender tube gap portion on a side of
the main tube portion.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a metal halide lamp using a
ceramic discharge tube.
[0003] 2. Description of Related Art
[0004] In metal halide lamps provided with a ceramic discharge
tube, there is less reactivity between a discharge tube material
and enclosed metals compared to metal halide lamps having a quartz
discharge tube, which has been in general use so far. Therefore, it
is expected that stable lifetime characteristics can be obtained
for the metal halide lamps using a ceramic discharge tube.
[0005] Conventionally, metal halide lamps having a discharge tube
in which both end portions of a transparent alumina tube are closed
by insulating ceramic caps or conducting caps are proposed as such
metal halide lamps (see JP 62-283543 A).
[0006] Further proposed are metal halide lamps having a ceramic
discharge tube having slender tube portions at both end portions of
a discharge portion and having a smaller diameter than the
discharge portion (see JP 6-196131 A). Electrically conductive lead
wires having an electrode at their tips are inserted at the slender
tube portions. The gaps between the end portions of the slender
tube portions and the electrically conductive lead wires are sealed
with a sealing material.
[0007] Such conventional metal halide lamps using a ceramic
discharge tube utilize the high thermal resistance of the ceramic
to raise a tube-wall load (lamp power per surface area of the
entire discharge tube) compared to metal halide lamps having a
quartz discharge tube, thereby improving the lamp efficiency. In
such metal halide lamps, a technology is proposed in which the
entire discharge tube is covered with a transparent protecting
cylinder, thereby raising the temperature of the discharge tube so
as to increase a vapor pressure of the enclosed metals and
preventing an outer tube glass from breaking when the discharge
tube is damaged.
[0008] In the metal halide lamps using a ceramic discharge tube,
the tube-wall load of the discharge tube is raised compared to
metal halide lamps having a quartz discharge tube, thereby
achieving high efficiency and high color rendition. However, in
order to realize high efficiency and high color rendition, it is
necessary not only to raise the tube-wall load but also to keep the
temperature in the discharge tube high. Accordingly, the
transparent protecting cylinder or the like is used to maintain
heat of the discharge tube.
[0009] On the other hand, in the metal halide lamps using a ceramic
discharge tube, leaks in the discharge tube sealing portion caused
by reactions of the enclosed metals with the sealing material and
the lead-in wire serve as a considerable cause for dimming or dying
out during the lamp lifetime. The conventional method for
maintaining heat of the ceramic discharge tube of the metal halide
lamps has had a problem in that, because the protecting cylinder
surrounds the entire discharge tube, the temperature of the
discharge tube sealing portion rises, leading to more reactivity of
the enclosed metals with the sealing material and the lead-in wire.
This increases the leaks in the discharge tube sealing portion
during the lamp lifetime.
[0010] In addition, the metal halide lamps using a ceramic
discharge tube have had a problem that the slender tube portions
and the sealing portions of the discharge tube are damaged easily
by a shock of dropping or the like.
SUMMARY OF THE INVENTION
[0011] It is an object of the present invention to solve the
problems described above and to provide a metal halide lamp that
suppresses leaks in a discharge tube sealing portion while
maintaining high efficiency and high color rendition, which are
features of a metal halide lamp using a ceramic discharge tube, and
that is tolerant of an external shock.
[0012] In order to achieve the above-mentioned object, a metal
halide lamp of the present invention includes an outer tube
containing the ceramic discharge tube, and a protecting cylinder
provided inside the outer tube so as to surround the discharge
tube. The slender tube sealing portion of the discharge tube is
exposed beyond the protecting cylinder.
[0013] Also, a metal halide lamp of the present invention includes
a discharge tube of a transparent ceramic in which a discharge
metal and a buffer gas are sealed, the discharge tube having
electrodes at both ends thereof, including a discharge portion,
slender tube portions provided at both ends of the discharge
portion into which feedthroughs including the electrodes and
lead-in wires are inserted, and slender tube sealing portions in
which gaps between the slender tube portions and the feedthroughs
are sealed with a sealing material; an outer tube containing the
discharge tube; and a transparent protecting cylinder provided
inside the outer tube so as to surround the discharge tube. At
least one of the slender tube sealing portions is exposed beyond
the protecting cylinder.
[0014] According to the present invention, heat is released
appropriately from the sealing portions while keeping the
temperature in the discharge tube high. Therefore, it is possible
to suppress leaks in the discharge tube sealing portion while
maintaining high efficiency and high color rendition.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a partially broken front view showing a structure
of a metal halide lamp in accordance with an embodiment of the
present invention.
[0016] FIG. 2 is a cross-sectional view taken along a line I-I in
FIG. 1.
[0017] FIG. 3 is a cross-sectional view showing a structure of a
discharge tube provided in the metal halide lamp described
above.
[0018] FIG. 4 is a plan view showing a structure of a support band
provided in the metal halide lamp described above.
[0019] FIG. 5 is a cross-sectional view showing the structure of
the support band provided in the metal halide lamp described
above.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] In the present invention, at least one of the slender tube
sealing portions is exposed beyond the protecting cylinder, and it
is more preferable that both ends of the slender tube sealing
portions are exposed beyond the protecting cylinder. The exposed
length preferably ranges from 0.5 to 10 mm. The exposed length of
shorter than 0.5 mm brings about less effect of decreasing the
temperature of the slender tube sealing portion. That of longer
than 10 mm causes an excessive decrease in the temperature of the
slender tube sealing portion, leading to more undesirable variation
of light colors.
[0021] In the metal halide lamp of the present invention, it is
preferable that the protecting cylinder is supported within the
outer tube by a support, and an elastic plate further is connected
to the support so as to support the slender tube portions.
Accordingly, the elastic plate is a metal, and thus a heat release
from the slender tube sealing portion and an insulation against a
heat from the discharge portion in the discharge tube are performed
via the elastic plate, making it possible to lower the temperature
of the sealing portion effectively. In addition, the slender tube
portions in the discharge tube are supported by the elastic plate,
thereby reducing a shock when the lamp is dropped and preventing
the discharge tube from being damaged. The support mentioned above
is for positioning the protecting cylinder in the outer tube, and
can be a plate-like object or a band-like object.
[0022] Furthermore, in the metal halide lamp of the present
invention, it is preferable that the slender tube sealing portions
are provided outside a portion to be supported by the elastic
plate. With this structure, a larger effect of the heat release and
the heat insulation described above can be achieved, and an effect
of suppressing leaks in the discharge tube sealing portion can be
improved as well.
[0023] The following is a description of an embodiment of the
present invention, with reference to the accompanying drawings.
[0024] A 70 W metal halide lamp illustrated in FIGS. 1 and 2, which
is an embodiment of the present invention, has a structure in which
a ceramic discharge tube 1 is rigidly supported by metal wires 6a
and 6b inside an outer tube 2 and a transparent protecting cylinder
3 is supported rigidly by a support band 7 in such a manner as to
surround the discharge tube 1. The support band 7 is fixed to the
metal wire 6a by welding. The support band 7 can support the
protecting cylinder 3 by holding four points on the outer periphery
of the protecting cylinder 3 and position the protecting cylinder 3
at the center of the outer tube 2 by bringing four corners of the
support band 7 into contact with an inner wall of the outer tube 2.
One end of the outer tube 2 is provided with a stem 4, which seals
the outer tube 2 airtight. Nitrogen is filled at 46.5 kPa in the
outer tube 2.
[0025] A predetermined amount of mercury, argon as a noble gas for
a starting gas, and iodides of dysprosium, thulium, holmium,
thallium and sodium as metal halides are sealed in the discharge
tube 1. Numeral 9 indicates a slender tube gap portion, and numeral
17 indicates a lamp base.
[0026] As is shown in FIG. 3, the ceramic discharge tube 1 includes
slender tube portions 19 on both end portions of a main tube
portion 8. The main tube portion 8 and the slender tube portions 19
are sintered into one piece with ring portions 18.
[0027] A feedthrough 20 constituted by an electrode 12 and a
lead-in wire 11 made of electrically conductive cermet having an
outer diameter of 0.7 mm is inserted into each of the slender tube
portions 19. The feedthroughs 20 are sealed with a sealing material
10 in the slender tube portions 19 so that the tips of the
electrodes 12 are positioned inside the main tube portion 8, and
slender tube sealing portions 5 are formed in the slender tube
portions 19. Electrode coils 13 are welded to the tips of the
electrodes 12. Numeral 14 indicates a mercury pellet, and numeral
15 indicates an iodide pellet.
[0028] In accordance with the structure described above,
Conventional Example A in which the protecting cylinder 3
surrounded the entire discharge tube 1, Structure B in which the
slender tube sealing portions 5 were exposed beyond the protecting
cylinder 3 by 2 mm, Structure C in which elastic plates 16 were
added to the support band 7 of Structure B so as to support the
slender tube portions 19 of the discharge tube 1 as shown in FIGS.
4 and 5, and Structure D in which the slender tube sealing portions
5 were provided outside a portion to be supported by the elastic
plates 16 in Structure C as shown in FIG. 5 were prepared. For
these structures, the occurrence of leaks in the discharge tube
sealing portions (sample number n=35) was examined after 6000 hours
of operation during lifetime. Table 1 shows the results of these
measurements.
1 TABLE 1 Structure Occurrence of Leaks (%) A 20 B 9 C 5 D 3
[0029] As becomes clear from Table 1, Structures B, C and D made it
possible to suppress the occurrence of leaks in the discharge tube
sealing portions to 50% or less compared to that of Conventional
Example A.
[0030] This was because, by exposing the slender tube sealing
portions 5 beyond the protecting cylinder 3, the temperature of the
slender tube sealing portions 5 decreased, leading to less
reactivity of the enclosed metals with the sealing material 10 and
the lead-in wire 11. The result for Structure C was attributable to
the further temperature decrease in the slender tube sealing
portions 5 caused by adding the elastic plates 16 to the support
band 7 so as to support the slender tube portions 19 of the
discharge tube 1. Moreover, the result for Structure D was
attributable to the further temperature decrease in the slender
tube sealing portions 5 caused by providing the slender tube
portions 5 outside the portion to be supported by the elastic
plates 16.
[0031] When Structures B, C and D were chosen, lamp characteristics
did not change very much and high efficiency and high color
rendition were maintained.
[0032] Next, drop tests were conducted for both cases with and
without the elastic plates 16 attached to the support band 7. In
the test method, lamps were wrapped up with two layers of cardboard
sheaths and then dropped from 60 cm. It was found that four out of
ten discharge tubes without the elastic plates were damaged, while
none of the ten tubes having the elastic plates were damaged.
[0033] As described above, according to the present invention, it
is possible to suppress leaks in the discharge tube sealing portion
while maintaining high efficiency and high color rendition of the
lamp and prevent the discharge tube from being damaged by the shock
of dropping or the like.
[0034] Although the electrically conductive cermet was used as the
lead-in wires 11 of the slender tube portion 19 in the above
embodiment, other materials having a thermal expansion coefficient
close to that of the discharge tube material may be used for the
lead-in wires instead of the electrically conductive cermet. Also,
a non-conductive ceramic cap may be used for the sealing portion.
Moreover, the main tube portion of the discharge tube and the ring
portions also may be molded in one piece, and then sintered into
one piece with the slender tube portions, so as to form the
discharge tube. Furthermore, the discharge tube may be used in
which the main tube portion of the discharge tube, the slender tube
portions and the ring portions are molded in one piece.
[0035] Although nitrogen gas was filled in the outer tube 2 in the
above-described embodiment, a mixed gas containing nitrogen may be
filled. For example, Ne (neon) gas can be mixed with nitrogen and
filled into the outer tube 2. When using such mixed gas, it is
preferable that the nitrogen gas accounts for at least 50 vol
%.
[0036] In the present invention, the ceramic material used for the
discharge tube is not limited specifically. For example, it is
possible to use sapphire as a single-crystal metallic oxide,
alumina (Al.sub.2O.sub.3), yttrium-aluminum-garnet (YAG) or yttrium
oxide (YOX) as a polycrystal metallic oxide, or aluminum nitride
(AlX) as a polycrystal nonoxide.
[0037] In addition, in the above embodiment, a hard glass was used
for the outer tube. However, the material used for the outer tube
in the present invention is not limited specifically, but can be
any known material.
[0038] As described above, the present invention can provide a
metal halide lamp that suppresses leaks in a discharge tube sealing
portion while maintaining high efficiency and high color rendition
of the lamp and that is tolerant of an external shock, and
therefore is valuable in industry.
[0039] The invention may be embodied in other specific forms
without departing from the spirit or essential characteristics
thereof. The embodiments disclosed in this application are to be
considered in all respects as illustrative and not restrictive, the
scope of the invention being indicated by the appended claims
rather than by the foregoing description, all changes that come
within the meaning and range of equivalency of the claims are
intended to be embraced therein.
* * * * *